Telephone-circuit.



A. E. BEACHUM.

TELEPHONE CIRCUIT.

APPLICATION FILED MAY 20. 19M.

noemto't Patented July 4;, 1916.

UNITED STATES PATENT OFFICE.

ALBERTA EGBERT BEACHUM, OF POLKTON, NORTH CAROLINA, ASSIGN OR OF ONE-HALF TO ROBERT STEELE, OF ROCKINGHAM, NORTH CAROLINA.

. TELEPHONE-CIRCUIT.

Specification of Letters Patent.

Patented July 4, 1916.

Application filed May 20, 1914. Serial No. 839,725.

To all whom it may concern:

Be it known that I, ALBERTA EGBERT BEAGHUM, a citizen of the United States, residing at Polkton, in the county of Anson and State of North certain new and useful Improvements in Telephone-Circuits, of which the following is aspecification, reference being had to the accompanying drawing.

This invention relates to improvements in telephone circuits and has for its object an increase-in efliciency of the transmitter.

The invention consists of a special induc tion coil, and a balancing resistance, and the interconnection of these with the transmitter and receiver circuits.

For the sake of illustration, the invention is shown in connection with a local battery telephone instrument, but it is obvious that same may be employed in connection with any transmitter circuit whether in an instrument or switchboard.

Figure l is a diagram showing a complete local battery telephone instrument, embodying my invention. Fig. 2 is a modification of Fig. 1. Fig. 3 is a view of the core showing the windings in section and, the connections, diagrammatically.

Like figures of reference denote the same parts wherever they are shown.

1, 2 and 3 denote the windings on a common core, constituting an induction coil. \Vinding l is similar to the primary winding of the ordinary induction coil usually employed. The inside end 4 of this winding is connected to the outside end 5 of the No. 2 winding. so that current passes through these windings in opposite directions, and thereby the magnetic influence of 1 on the core is neutralized by that of 2.

I find that a coil with a comparatively small core gives the best results, although the dimensions and relative position of the windings may be varied within wide limits. I obtain very good results with a coil having the winding 1 next the core, winding 3 over the No. 1, and winding 2, outside.

Winding 1 may consist of 160 turns of No. 22 B & S gage single cotton covered wire. finding 3 of 2500 turns of No. 30 B & S gage single silk covered wire and winding 2 of 160 turns of No. 22 B & S gage single cotton covered wire, all wound in the same direction.

Winding 1 is included serially in circuit Carolina, have invented with the transmitter 6, a suitable source of energy such as the battery 7, and the switch hook contacts 8 and 9. A balancing reslstance 10 is placed in series with winding 2, which combination is bridged around winding 1 and the transmitter, as shown. I find that under ordinary conditions a resistance approximating the average mean resistance of the transmitter is satisfactory.

The remaining portions of the telephone circuit such as the receiver 11, the genera-- tor l2 and ringer 13 are connected in any suitable manner.

A modification of described is shown in Fig. 2 and consists in bridging thebalancing resistance 10 in series with winding 2, across the battery, transmitter, and winding 1, which is accomplished in the case of a telephone instrument by the employment of the extra contact 14 in the switch hook.

In operation, the hook contacts being closed by the removal of the receiver from. the hook, current flows through the transmitter 6 and winding 1 of the coil, and also through the balancing resistance 10 and winding 2. Windings 1 and 2 being wound in reverse direction in relation to their common core, or oppositely connected so that. they oppose each other, and the resistance 10 being approximately equal to transmitter 6, thecore of the coil is maintained in a magnetically unbalanced condition, which I find to be particularly susceptible to the impulses produced on the flowing current by the transmitter. The core being maintained in a critically unbalanced condition in respect to its hysteresis curve, very slight changes in the resistance of the transmitter cause powerful changes in the secondary currents produced.

It is known that the action of a transmitter in varying or undulating the current in the primary circuit, sets up an action, to the presence of the iron core, which in the case of very large variations, causes the core to reach a point of oversaturation which actually impedes or hinders the production of powerful free currents in the secondary. This condition is eliminated by my invention: What I claim as new, and desire to secure by Letters Patent is:

A telephone circuit, an induction coil comprising a core relatively long inaproporthe arrangement just i owing tion to its cross section, a primary winding next the core, a secondary Winding over said primary Winding and having a large nun1- her of turns, a second primary Winding over "said secondary winding and having the same number of turns as said first mentioned Winding, a circuit including a transmitter, a source of energy and one of said primary windings, a circuit including a re- 10 ceiving device and said secondary Winding,

and a circuit including said second primary winding and balancing resistance being bridged across said first mentioned primary Winding.

In testimony whereof I hereunto aflix my 15 

